POLYMERS
FE SEM –I
Engineering Chemistry-I
POLYMERS
• Polymers are macromolecules formed by linking together of a large
number of small molecules called monomers. The polymers are
giant molecules with high molecular masses. For example, the
monomer ethylene gets linked with many other ethylene molecules
to form polyethylene, or large number of vinyl chloride molecules
combines to form polyvinyl chloride.
• The single repeating unit is called as monomer, and the resultant
high molecular weight compound is called as polymer.
POLYMERS
POLYMERS
POLYMERS
• On the basis of this physical property, the polymers with high
degree of polymerization are known as high polymers while those
having comparatively low degree of polymerization are known as
oligopolymers. The molecular weights of polymers are generally in
the range of 5000 to 200,000. Hence, these are also known as
macromolecules.
• The total number (n) of single monomer units combined together
to form a polymer is known as degree of polymerization (DP). DP
affect physical properties of polymers.
CLASSIFICATION
• i) Based on source:
• a) Natural: e.g starch, cellulose, protein
• b) Semi synthetic: Nitro cellulose
• c) Synthetic: Polythene, polyvinyl chloride
CLASSIFICATION
• ii) The nature of monomer
• (a) Homo-polymers: A polymer containing identical monomers.
•
A-A-A-A
•
• (b) Co-polymers are the compounds formed by two different small
molecules. For example in polystyrene butadiene. One molecule of
butadiene combines with one molecule of styrene. The product
obtained acts as a monomer to get the polymer.
•
A-B-A-B-A-A-B
• iii) On the basis of arrangement of monomeric units in polymer, these are
named as linear, branched or cross — linked (three dimensional
structures),
•
•
•
•
Some examples of linear high polymers are rubber,
polyethylene, cellulose, polyvinyl acetate
Polyethylene may also have branched chains.
The vulcanised rubber is the best known example of cross-linked
polymers in which -S-S- cross links are joined irregularly. Due to cross
linking polymer structure becomes three dimensional cross linked or
network polymer. This makes the polymer very hard and rigid.
CLASSIFICATION
Branched polymer
CLASSIFICATION
• iv)Based on atoms- If the main chain of the polymer is of same atoms, it is known as homochain polymers while if is of different atoms it is known as hetero polymer.
• e.g.
-C-C-C-C-CHomochain polymer
•
-C-O-C-O-C-O- Heterochain polymer
• v) Co-polymer is named as regular or irregular on the basis of arrangement.
• e.g. -A-B-A-B-A-B-A-B-A- Regular
•
-A-B-B-A-B-A-A-B-B- Irregular
•
•
—A.—B—A—B—A—B-A
Linear co-polymer
•
•
Branched chain homopolymer
•
CLASSIFICATION
• If co-polymer chain possesses relatively long sequence of like
monomers, it is called as block co-polymer where as if co-polymer
possesses branched structures in which the monomer segments are
not in same sequence on branch and backbone, it is known as graft
co-polymers.
• vi) Based on effect of heat polymers are of two types
• Thermoplastics and Thermosetting
CLASSIFICATION
CLASSIFICATION
CLASSIFICATION
• vii) Polymers are also classified on the basis of configuration of
macromolecule known as Tacticity of polymers n following ways
• a) Isotactic polymers
• In isotactic, the head to tail configuration in macromolecule
with respect to functional groups is iso, i.e. all the functional groups
lie on the same side of the chain.
CLASSIFICATION
• b) Atactic polymers
• In atactic, the head to tail configuration is random i.e. the functional
groups are arranged randomly.e.g polypropylene
• c) Syndiotactic polymers
• Arrangement of side group in alternating fashion is called
syndiotactic polymer. e.g gutta percha
CLASSIFICATION
• b) Atactic polymers
• In atactic, the head to tail configuration is random i.e. the functional
groups are arranged randomly.e.g polypropylene
• c) Syndiotactic polymers
• Arrangement of side group in alternating fashion is called
syndiotactic polymer. e.g gutta percha
CLASSIFICATION
CLASSIFICATION
• Vii-These are examples of homo-organic polymers. Other examples
of organic polymers are polysaccharides, proteins, DNA, viii) On the
basis of chemical composition, the polymers are also called either
organic or inorganic polymer. Generally in organic polymers, carbon
with or without N, S, O, forms the skeleton while in inorganic, other
elements form the skeleton.
• e.g Polyethylene., [ - - - - H2 C - CH2 ------)
•
e.g. Polysilanes
• RNA etc. Man made organic polymers include PVC, PP, PVA, PF,
UF, polyesters, polyamides, polyurethanes, synthetic rubbers etc.
CLASSIFICATION
• Inorganic polymers are those in which atoms other than carbon
form the skeleton of polymer. Polysiloxanes or polytitoxane0 are the
examples of polymers where side chain may be of organic nature.
They are also known as elemento-organic or hetero-organic
polymers. Polysilanes are purely inorganic in nature. Other
examples of this class are MgO polymer or hydrogen borons.
•
•
[- - -Mg -O-Mg-O-Mg---]
Magnesium oxide polymer.
•
CLASSIFICATION
POLYMERIZATION
• The reaction of monomers to form a polymer is
known as polymerization. The polymers are formed
mainly by
• i) Addition polymerization (Chain polymerization).
; ii)
Condensation polymerization (Step
polymerization).
• iii)Copolymerization
POLYMERIZATION
•
I) Addition
or Chain Polymerization-
• The word chain indicates elongation of carbon skeleton to form a polymer. Generally such a polymerization involves the
(C = C) link in monomer. The double bond breaks and as a result two single bonds on either side of each carbon are
formed and thereby elongation of carbon chain continues. The product of this type of polymerization is exact multiple of
monomer number, having no by-product or loss of any molecule.
Thus,
• a. Addition polymerization is undergone by monomers having C = C linkage, e.g.
•
ethylene, vinyl chloride, propylene, butadiene, styrene etc.
• b. The rate of reaction is very high.
;
• c. The polymerization reaction involves three steps such as
• a) Initiation.
• b) Propagation or branching and
•
c) Termination.
POLYMERIZATION
POLYMERIZATION
POLYMERIZATION
• ii) Condensation Step Polymerization• The monomers having certain functional groups such as -OH, COOH, - NH2 etc. show the tendency to undergo polymerizations by
the elimination of one molecule of a simple by-product such as H2O,
HC1, salt or alcohol etc. Unlike addition / chain polymerizations,
polymer loses simple molecules at every combination, as a result
does not have exact multiple number of monomer units.
POLYMERIZATION
Thus,
• a. Condensation polymerization is undergone by the monomers which
possess functional groups.
• b. Generally monomers are like acids, amines, alcohols, phenols, carbonyl
compounds etc.
• c. This type of polymerization occurs stepwise, hence the rate of
polymerization is comparatively slow, it depends on kind of catalyst the
temperature and the time of reaction
• Ex: Nylon 66 Phenol formaldehyde
POLYMERIZATION
• iii) copolymerization:
• It is a joint polymerization of two or more monomers. High
molecular weight compounds obtained by copolymerization are
called copolymers. For example butadiene and styrene
copolymerizes to give GRS-rubber or Buna-S
• Ex:Buna S
POLYMERIZATION
PLASTICS
• Polymers are called as plastics since they can be moulded to desired
shape by application of heat and pressure.
• Classification of Plastics
• On the basis of setting manner in final stage of manufacture, the
plastic materials are plastic articles which are classified in two
classes viz. thermo setting and thermo plastic.
PLASTICS
• a)Thermo Setting Plastics: These are the polymers which on heating
change irreversibly into hard and rigid materials. This melt of
polymer when set into a mould to form an article, is almost a
permanent set. On reheating the article does not soften again. They
are hence known as thermo hardening plastics or permanent setting
resins and during moulding acquire three dimensional cross linked
structure with strong covalent bonds. On reheating, these bonds
retain their strength and hence such a plastic does not soften on
reheating.
PLASTICS
• Thermo setting plastics can not be reclaimed from waste due to
their irreversibility. They are hard, strong and brittle than thermo
plastics. The method by which these are formed is called as
condensation polymerization. They are insoluble in almost all
organic solvents, due to their cross linked three dimensional
structure. Phenol formaldehyde / bakelite, amino plastics and alkyl
plastics, epoxy plastics, silicon plastics etc are the best known
examples of thermosets.
PLASTICS
•
) Thermo Plastics: These show reversible change on heating i.e they soften on heating
but regain their original properties on cooling. They gain or lose hardness with rise or
fall in temperature. Their chemical nature does not get affected even on repeated
heating and cooling, i.e the changes are more of physical nature. If these resins are
softened, they retain their softness at that temperature. These resins can be reclaimed
from waste, and they are soft, weak , less brittle as compared to former type of
plastics resins. The method usually used to manufacture is addition polymerisation.
They are generally long linear polymer with occasional or no cross linkingng. They
are soluble in specific organic solvents, nples of this class of resins are cellulose nitrate,
polyacrylates, ethyl cellulose , polyvinyl resins, or polystyrene resins, polyamides
(nylons), 'rc'.yethers, polypropylene, polyethylene etc.
(b
PLASTICS
TheThrmosoftening Plastics
These are are long chain linear polymers with negligible formed by
Th Thermosetting or Thermohardening Plastics
These are formed by condensation polymerization
addition polymerization
These have linear and branched structure
These have three-dimensional network structure with
number of cross links
They have low molecular weight as compared to
They have high molecular weight as compared to
therrmosetting
thermo softening plastics
type plastics
They are usually soft, weak and less brittle
They are usually soluble in some organics solvents
They are usually hard, strong and more brittle
Due to strong bonds and cross links, they are insoluble
in all organic solvents.
They get softened on reheating readily because
The crosslinks and bonds retain their strength on
secondary forces between the individual chain
heating and hence, they do not soften on heating.
ch
can break easily by heat or pressure.
By reheating to a suitable temperature they can be
softened, reshaped and thus reused
They retain their shape and structure even on heating.
Hence, they cannot be reshaped and reused.
PLASTICS
PLASTICS
COMPOUNDING OF PLASTICS
• Plastics are manufactured synthetically using raw materials mostly from natural gas
and petroleum, or from coal mines, forests, farms and paper and textile mills.
• In addition to the raw materials chosen the plastics are generally compounded with
some other substances so as to impart certain specific properties to the product
Usually such moulding compositions are prepared from two or more of the following
material groups.
• Binders or resins.
• Fillers or extenders.
• Pigments or dyes or colouring agents.
• Catalysts or accelerators.
• Plasticizers.
• Lubricants.
• Stabilizers.
COMPOUNDING OF PLASTICS
• 1) Binders hold the other constituents together during manufacture.
Usually natural or synthetic resins or cellulosic derivatives are used
as binders, which are high molecular weight substances. Binders
influence the properties of plastics. The type of the treatment
during moulding operation also depends upon binders. If binder
used has comparatively low molecular weight, then plastic article
gets moulded easily and vice versa.
COMPOUNDING OF PLASTICS
• 2) Fillers or Extenders impart better tensile strength hardness of plastic
material, finish workability opacity etc. They reduce shrinkage and brittleness.
They also reduce cost of the plastic per unit weight. The fillers may be of
organic or inorganic origin.The fillers which are added only to improve the
mechanical strength of the plastic are called as reinforcing fillers.
Example
•
Carborundum (silicon carbide), Quartz/ mica improve hardness of plastic
material whereas, barium salts help to make the plastic impervious to x-rays.
The heat and corrosion resistance can be improved by adding asbestos.
• Other examples are Wood flour, cotton pulp, paper pulp, carbon black,
graphite, powdered rubber,
COMPOUNDING OF PLASTICS
• 3) Pigments / dyes / Colouring matter imparts desired colour to plastic.
Organic dyestuffs and inorganic pigments are used for this purpose in
small proportion.
• 4) Catalyst or accelerators are used to increase the rate of polymerisation
of fusible resin binder to form cross linked infusible form during
moulding operations. Generally thermosetting plastics involve use of
catalyst
normally
an
acidic
or
basic
catalyst
expending upon the type of thermosets. The catalyst is added in small
quantities. Commonly used catalysts are hydrogen peroxide, benzoyl
peroxide, metallic oxides etc.
COMPOUNDING OF PLASTICS
• Plasticizers help to increase the plasticity of the plastics. The adequate quantity
of plasticizer also hel.ps to soften the plastic at comparatively lower
temperature. The.functions of plasticizers are to Enhance flexibility or plasticity.
decrease brittleness. reduce the viscosity of resins so that they can be moulded
even at high temperature and pressure. lower softening temperature. lower
moulding or remoulding temperature. Plasticizers are not used in thermosets,
they are added in thermo softening
• They reduce intermolecular attraction and thereby increases tendency of sliding
or moving. Thus the plastics which are plasticized possess high percentage of
flexibility. The commonly used plasticizers resins only.
• Plasticizers occupy the position with uniform distribution between the polymer
molecules. This type of dispersal of plasticizers reduces the forces are
lubricants, camphor, alkyl phosphates, vegetable oils, fatty acids and some
phosphates (tricresyl phosphate, triphenyl phosphate). They are added to the
extent of 8-10 % of the total bulk of plastic.
COMPOUNDING OF PLASTICS
• Lubricants help during moulding operations, especially during low
or room temperature moulding. The use of lubricants imparts
flawlessness, and glossy finish to the plastic products. This is
because the lubricants tend to get dispersed towards outer surface
of the finished product, hence during moulding, they form a layer
between the article and mould. This layer prevents the plastic
material from sticking to the surface of the mould, and thereby
facilitating the moulding operations. Commonly used lubricants are
soaps, or esters of fatty acids such as oleic and stearic acids or
waxes
COMPOUNDING OF PLASTICS
• Stabilizers help to improve thermal stability of the plastic. These are
required especially in the processing stage for plastics, which have
tendency to decompose or change their colours at moulding
temperatures.a) opaque moulding compounds like salts of lead e.g.
white lead, lead chromate. b) transparent moulding compounds like
stearates of lead , cadmium and barium.
FABRICATION OR MOULDING OF PLASTICS
• The fabrication is the process in which the prepared resins in the
form of granules or powder are converted into desired shape by
using various machines or moulds. There are many ways by which
the compound materials are transformed into famaliar finished
articles. The basic principle involved in this is partially melting
(softening) resinous mass by the application of heat. These softened
resins are further compressed in dies, moulds with the help of high
pressure to get the desired shape.
FABRICATION OR MOULDING OF PLASTICS
• In this case of thermosetting plastics moulded hot 'plastic is
ultimately solidified through further [polyermisation, called curing
or setting stage while it still in the mould. In the case of
thermosoftening lastic, the moulded plastic material is further
cooled chilled for solidification of article, thermosoftening plastic
material, injection, extrusion, blow moulding, vaccum forming are
usually used. For thermosetting compression moulding, transfer
moulding are generally employed.
COMPRESSION MOULDING
Top moulding part (male die)
COMPRESSION MOULDING
• This process consists of pressing the molten resinous material into
the shape by the use of moulds, heat and pressure.
• Predetermined quantity of resin powder or pellets is preheated to about
120 °C before the cavity is filled with it. After charging the two parts of
mould are carefully brought together under low pressure. It is then
pressed by hydraulic pressure. Pressures of about
• 10,000 p.s.i are used. This pressure and heat make the resin to melt and
flow, thereby filling the cavities between the two parts of the mould.
Than the mould is kept for the specified time Than curing is done either
by heating for thermoseetts or cooling in case of thermosofts
INJECTION MOULDING
INJECTION MOULDING
• It is one of the most widely used processes for thermoplastic
raw materials into products. It is fundamentally simple and
easy to operate and capable of producing a very wide range of
industrial and domestic articles
• In this process a predetermined quantity oil granular or powdered
resin is fed into a cylinder from where it is injected at a controlled
rate through a nozzle into the tightly locked mould means of a screw
arrangement or by piston plung shown in the Fig.. Pressure upto
1758 kg/ci used for injections. The mould is kept cold so that the
hot plastic cures and become rigid
INJECTION MOULDING
• This method is the most widely used for moulding thermoplastics
because of high speed production mould cost, very low loss of
material and finishing cost. However, there are limitation design of
articles to be moulded because many number of cavities cannot be
filled simultaneously.
TRANSFER MOULDING
TRANSFER MOULDING
• It is a method which uses the principle of injection molding and is used
for thermosetting material when relatively intricate designs are required
of fabricated products This transfer moulding is a combination of
injection and compression molding, In this molding powdered resins
are placed in heated chamber, maintained at a minimum temperature
due to which the powdered resins just begins to become plastic. This
plastic material is then injected through orifice into the mould by
plunger, working at high pressure. Due to which high friction develops at
the orifice, the temperature of the material at the of ejection from the
orifice rises to such an extent that moulding powder becomes almost
liquid, consequently it flows quickly into the mould, it is heated upto the
curing temperature.The moulded article is then ejected
•
TRANSFER MOULDING
Advantages;
• 1.Intricate shapes not attainable by compression moulding can readily be
produced.
• 2.Article produced is free from flow mark.
• 3.Even thick pieces cure almost completely and uniformly.
• 4.Finishing cost of fabricated article is almost entirely eliminated.
• 5.Blistering is almost eliminated, since air and excluded gases are
expelled in the plasticizing chamber itself.
• 6. Mould cost is less, since it involves very low abrasive action.
• 7.Fine wires and glass fibres can be inserted into the mould.
EXTRUSION MOULDING
EXTRUSION MOULDING
EXTRUSION MOULDING
• It is mainly used for continuous manufacturing articles with
uniform cross sectional area of thermoplastic resins.For example
tubes,rods,strips,insulated cable materials. In this
method dry
moulding powder is first fed through hopper into the heated
chamber which has a revolving screw. the screw is rotated the
molten material is forward through the small orifice of the die to
continuous uniform shaped articles. When it leaves the orifice, it is
allowed to pass through water for solidification of plastic material.
CONDUCTING POLYMERS
• Polymeric materials having conductivities on par with metallic
conductors are called as conducting polymers. Polymers having
conjugated double bond are conducting in nature due to presence of
delocalized pi electrons. Conductivities as high as 1.5 X 107 ohm-1 m-1.
CONDUCTING POLYMERS
CONDUCTING POLYMERS
CONDUCTING POLYMERS
• Conducting polymers are of four types: 1) Intrinsically conducting 2)
Doped conducting 3)Extrinsically conducting 4)Co-ordination conducting
polymers
• Intrinsically conducting polymers(ICP)
or conjugated П- electrons
conducting polymer is a polymer whose backbones or associated groups
consist of delocalized electron –pair or residual charge. Such polymers
essentially contain conjugated П- electrons backbone which is responsible
for electrical charge. In an electric field ,conjugated П-electrons of the
polymer get excited ,thereby can be transported through the solid
polymeric material.Overlapping ( of conjugated П-electrons ) over the
entire backbone results in the formation of valence bands as well as
conduction bands which extends over the entire polymer molecule
.Presence of conjugated П-electron in a polymer increases its
conductivity to a larger extent .
CONDUCTING POLYMERS
• Important commercially produced conducting polymers :
• Polyacetylene
polymers
.e.g.
poly-p-phenylene,
polyquinoline,polyphenylene-co-vinylene,poly-m-phyenylene
sulphide ,etc.
• ii) With condensed
aromatic rings ,e.g
ployaniline,
polyanthrylene,polyphenarnthrylene,etc.
• iii) With aromatic heteroaromatic and conjugated aliphatic units,
e.g. polypyrrole,polythiophene,polyazomethine,ploybutadienylene
,etc.
CONDUCTING POLYMERS
• 2)Doped conducting poiymers are obtaining by exposing a polymer
to a charge transfer agent in gas/solution phase.Conductivity of
intrinscically conducting polymers can be increased by creating
either positive or negative charge on the polymer backbone by
oxidation or reduction.
• A) p-doping-In this an intrinscically conducting polymer is treated
with lewis acid where oxidation takes place. Common lewis acid are
I2,Br2 etc
• 2(C2H2)n+3I2----.>.2(C2H2)n++I3-
CONDUCTING POLYMERS
• B)n-doping--In this an intrinscically conducting polymer is treated
with lewis base where oxidation takes place. Common lewis acid are
Li,Na etc.
• -CH=CH-CH=CH+B----.>-CH=CH-C-H=CH
B+
CONDUCTING POLYMERS
• 3)Extrinscically conducting polymersare the polymers whose
conductivity is due to presence of externally added ingredients.They
are of two types;
• A)Conductive element filled ploymers-Polymer act as a binder to hold
the conducting elements eg carbon black,metal oxide.
• B)Blennded conducting polymers-A conventional polymer is blended
with conduting polymers.
CONDUCTING POLYMERS
• 4)Co-ordination conducting polymers-It is a charge transfer complex
containing polymer obtained by combining a metal atom with poly
dentate ligand.
Applications of Conducting Polymers
• 1.In rechargeable light weight batteriesbased on perchlorate doped
polyacetylene Li system.These are 10 times stronger than
conventional lead storage batteries
• 2.In wiring in aircrafts and aerospace component.
• 3.In transistors and diodes.
• 4.In elcctromagnetic screening materials
• 5.In photovoltanic devices.
• 6. In molecular wires and switches
Glass Transition Temperature:
• The temperature at which the polymer experiences the transition
from rubbery to rigid states is termed the glass transition
temperature (Tg) .These sequences of events occurs in the reverse
order ,when a rigid glass at a temperature below Tg is heated .
• Glass transition temperatures : Glass transition temperature is
important parameters relative to applications of polymers. It
define respectively ,the upper and lower temperature limits for
numerous applications , especially for semi crystalline polymers.
Moreover , they also influence the fabrication and processing
procedures for polymers and polymer-matrix composites .
Factors influencing glass transition temperature:
• Upon heating through the glass transition temperature ,the amorphous solid
polymers transforms from a rigid mass to a rubbery state and the molecules
which are virtually frozen in position below Tg begin to experience rotational
and translational motions above Tg.
• 1. The presence of bulky side groups (this may be confirmed from Table 1 ,the
respective values for polypropylene and polystyrene are -18ºC and 100˚C).
• 2. Polar side atoms or groups of atoms {this may be confirmed by comparing Tg
values for polyvinyl chloride and polypropylene (87ºC versus -18ºC) }.
• 3. Double –chain bonds and aromatic chain groups which tend to stiffen the
molecular backbone
• .4. Increasing the molecular weight also tends to raise the glass transition
temperature
Factors influencing glass transition temperature:
• 5. A small amount of breaching will tend to lower Tg; on the other
hand a high density of branches reduces chain mobility and
elevates the glass transition temperature .
• 6. As crystallainity increases Tg also increases.
• 7. As cross linking increases Tg also increases
• 8 Effective Plasticizers – Addition of plasticizer decreases Tg of the
polymer .
Viscoelasticity of Polymers:
• An amorphous polymers behave like glass at lower temperature ,a
rubbery solid at intermediate temperature and a viscous liquid at
higher temperature .For intermediate temperature the state is
rubbery solid .That exhibits the combined properties of two
extremes of solid and liquid ,the condition is called as viscoelasticity
.This material exhibits both viscous and elastic characteristics .
• Viscous material like honey resist strain linearly with time when
stress is applied .Elastic materials strain instantaneously when
stretched and quickly return to their original state once the stress is
removed.
Viscoelasticity of Polymers:
Viscoelasticity of Polymers:
• Polymer show a behavior in between elastic solids and flowy liquids.
These properties depend on temperature and time duration .As
elastic solids restore shape after removal of external forces ,while
in case of viscous liquids there is no definite shape hence when
external forces are applied it flows out irreversibly Viscoelastic
materials have elements of both these properties .Viscoelasticity is
molecular rearrangement. Under stress polymer chains change
position (creep) and polymer remain in solid state .
Viscoelasticity of Polymers
Poly methyl meth acrylate(PMMA)
• Preparation
Poly methyl meth acrylate(PMMA)
•
•
•
•
Properties1. It is transparent and having good optical properties.
2.Softening temperature is 130-140oC.
3.It has low scratch resistence.
• Uses• 1.It is used for making lenses, artificial eyes and optical parts of
instruments.
• 2.It is used for making window glasses.
• 3.It is used for making scientific models.
Kevlar
Kevlar
• Properties• 1.Exceptionally strong,5 times stronger than steel and 10 times
stronger than aluminium.
• 2. It is highly stable and flexible.
• 3.It is stable at -196oC
• 4.It degrades by UV radiation.
Kevlar
• Uses• 1.It is used in aerospace and aircraft industries.
• 2.It is used for making car parts such as tyres and brakes.
• 3.It is used for preparation of ropes,cables.protective cloths,helmets
etc.
Molecular weight of polymers
• It is very important phenomena,sice physical properties of macro
molecules depends on M.W.Higher the M.W. ,tougher the
polymer.The M.W and its distribution decides the viscous and elastic
behavior of molten molecule.
• Methods of M.W. Determination• (1)Number -average M.W.
• (2)Weight average M.W.
Number average M.W.
Weight average M.W.
Polydispersity Index
• It is the ratio of weight average M.W and number average M.W.
ie Mw/Mn
• If value of polydispersity index is 1,polymer is identified as
monodispersed,where consisting molecules have identical mass.If
value is 2,polymer is identified as polydispersed,where consisting
molecules have different mass.